updates for Order and Product common functionality
work on simple order
Merge pull request #4 from inspiran/master

started fixing tests and adjusted the invoice manager
reorganize PricingManager tests
Relocated remaining tests
Fixed billing tests and adjusted headers
Added invoice and invoice item mapping
Fixed an order test
fixes
Merge pull request #5 from iampersistent/feature/simple-billing

Feature/simple billing
Adjusted mapping to allow multiple product descriptions